Car shuts off randomly, won't start until engine is cold

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  • LounsRacingInc
    replied
    Originally posted by D_bender
    Ok. Both sensors are good, Ignit ion coil does light up. I just put in a new coil, Cap and rotor, and crank sensor
    Does it light up and stay lit? or does it flash when cranking, you should see a very distinct flashing while cranking

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  • LounsRacingInc
    replied
    Originally posted by dnguyen1963
    Not always true...when things expand, vacuum leaks can develop at places like the throttle body or valve cover.
    You are both correct, vacuum leaks could be caused by heat or cold (although heat is not as common as cold) but if you don't have switching on the negative side of the coil the issue is not vacuum related, its electrical and has to do with a sensor or wire that is effected by heat

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  • dnguyen1963
    replied
    Originally posted by Kershaw
    Things expand when warm, usually vacuum leaks are present when cold, but not warm. That doesn't make sense to me. Also, the fact that it doesn't even try to start at all, like no cranking, means that it's probably not a vacuum problem. Sounds more like a grounding issue. The hot/cold thing doesn't make sense though.

    The only thing I can think of is heat soak. A hot wire will have a greater resistance than a cold wire. So it may be that something is getting funky when the hot engine heat soaks the engine bay.
    Not always true...when things expand, vacuum leaks can develop at places like the throttle body or valve cover.

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  • Kershaw
    replied
    Things expand when warm, usually vacuum leaks are present when cold, but not warm. That doesn't make sense to me. Also, the fact that it doesn't even try to start at all, like no cranking, means that it's probably not a vacuum problem. Sounds more like a grounding issue. The hot/cold thing doesn't make sense though.

    The only thing I can think of is heat soak. A hot wire will have a greater resistance than a cold wire. So it may be that something is getting funky when the hot engine heat soaks the engine bay.

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  • dnguyen1963
    replied
    Originally posted by D_bender
    I changed the ignition coil with a new one, also I've tried to use a different dme and still won't start when warm
    Does it start cold? If it does then I suspect vacuum leaks are causing the warm no-start.

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  • D_bender
    replied
    ????

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  • D_bender
    replied
    What else could cause this?m?

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  • D_bender
    replied
    I changed the ignition coil with a new one, also I've tried to use a different dme and still won't start when warm

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  • dnguyen1963
    replied
    Borrow a working DME from someone. I suspect that the ignition coil is the culprit, but you said you tested it already.

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  • D_bender
    replied
    What Else Could It be?

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  • D_bender
    replied
    I tested for spark and I am not getting spark

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  • D_bender
    replied
    Ok. Both sensors are good, Ignit ion coil does light up. I just put in a new coil, Cap and rotor, and crank sensor

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  • dnguyen1963
    replied
    Are you sure your car has no vacuum leaks?

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  • LounsRacingInc
    replied
    If the sensors both turn out good, get a 12v test light, (if you don't have one autozone/advance/napa/etc. sell them for like $5) hook it to a ground and then hold it on the negative terminal on the coil. Have a buddy crank the engine, you should see it flicker. If it does, then you know the issue is with a sensor other than the CPS, if it doesn't then the ecu is not grounding the coil like its supposed to.

    Edit: I would actually do this test first

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  • LounsRacingInc
    replied
    Check BOTH the speed reference and the crank position sensor, they are located on the bell housing by the slave cylinder, unplug them and test the resistance, they should be at 960 ohms +/- %10 (unfortunately I cant remember the wire colors to test). Using the same pins, also test for AC VOLTAGE....AC, not DC, have a buddy crank the motor over, you should see greater than 250mv AC. do both tests when the motor is cold, then start it and warm it up until it dies, then do the tests again. I'm willing to bet your sensors work fine when the motor is cold and then start to lose their response when warm

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